Right now we don't have a way to differentiate between whether a server can
serve ellipsis or not. The way we check whether a server is narrow enabled is by
checking bundle2 capability which does not scale outside of bundle2 world.
The goal is to use have wireprotocol commands just like remotefilelog for
widening the narrow clone, atleast in non-ellipses cases. Having a server
capability will help there as we can't rely on bundle2 capability there.
Also having a server capability is neat than having a bundle2 capability.
There are lot of things we can optimize locally on the client side by knowing
before hand that whether the server supports ellipses or not.
This will also help us in making sure that a client ellipses repo does not
communicate with a server repo without ellipses.
I'd rather not include "narrow" in the name. It doesn't necessarily require narrowness. You can imagine using ellipsis nodes to achieve a shallow clone that still has all paths.